quantize test: quiet overflow warning
quantize test: quiet overflow warning

Promote the result of RandRange to signed

Change-Id: I89313cace3bcbe9af96946bef00b6857fc48b128

webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx